4X DAC Design using Atmega16 and AD7528 IC

I am trying to develop DAC circuitry for Atmega 16 since Atmega16
doesn't have in-built feature of DAC. The circuitry design will be 4X
DAC design using AD7528 DAC Chips. To my understanding,the 4X DAC
circuit would be using 11 ports lines of Atmega16 where PortC0-PortC7
would be input to the 8-bit parallel AD7528 chip and 3 ports lines
(PortD0-Port2)would be used as control line inputs. The requirement of
this DAC circuit is that it would produce variable voltage (0DVc -
10DVc) at fix current of 25mA. I will plan to locate Op Amp in the
output of every AD7528 DAC chip.

I am not trying to ask anyone to do homework for me but I may treat
here as a resource to gain ideas for the development I am working on.
I will appreaciate anyone helping me by having discussions and making
suggestions related to this topic. Kindly show me any schematic/codes/link related to
this topic if u know any. Best Regards.

Why dont you try using a pwm output. Where you can vary the duty cycle, which in turn can be used to vary the voltage across a resistor connected across the PWM output pin and ground. Hence u get voltage variation between 0-5v. But this can be amplified using an opamp to whatever range you would require.

I had tried this earlier and it works pretty well!! But had not tried it with the opamp..